Field of the Invention
The present disclosure relates to an image processing apparatus for forming an image based on the electrophotographic process, and a method for controlling the image processing apparatus.
Description of the Related Art
In an electrophotographic image forming apparatus such as a laser beam printer and a copying machine, an exposure unit emits optical beams according to an exposure signal, forms an electrostatic latent image on the surface of a photosensitive member, and develops the electrostatic latent image through toner adhesion thereto. As an exposure method employed in the exposure unit of this electrophotographic image forming apparatus, the light emitting diode (LED) exposure method and the laser exposure method are known. In an LED exposure type image forming apparatus, light emitted from LED elements serving as light emitting elements is condensed on a photosensitive drum by lenses, respectively. A plurality of the LED elements is arranged in the longitudinal direction of the photosensitive drum, and a plurality of the lenses is respectively arranged in the longitudinal direction of the photosensitive drum between the LED elements and the photosensitive drum. A laser exposure type image forming apparatus includes a light source unit for emitting laser light from a semiconductor laser element as a light emitting element, and a deflect and scan unit for deflecting the laser light from the light source unit for scanning by using a polygon mirror. The laser exposure type image forming apparatus further includes a plurality of lenses for guiding the laser light from the light source unit to the deflect and scan unit, and focusing the deflected and scanned laser light on an image bearing member by the deflect and scan unit.
In the LED exposure type image forming apparatus, since reducing the lens size to about the pixel pitch is difficult, the arrangement interval of the lenses is larger than that of the light emitting elements. Accordingly, because of the difference in positional relationship between the optical axis of each light emitting element and the optical axis of each lens, a plurality of spot areas (areas irradiated with the light emitted from the light emitting elements via the lenses) is distorted in shape in respectively different directions. In the laser exposure type image forming apparatus, spot areas are distorted in shape in different directions according to the longitudinal position on the photosensitive drum. Such spot areas distorted in shape in different directions cause a problem that periodical density nonuniformity occurs in an output image.
Japanese Patent Application Laid-Open No. 2009-179062 discusses a technique for correcting the energy of the light emitted from each light emitting element to provide a uniform size (diameter) of distorted spot area in the distortion direction.
However, in the technique for correcting the energy of the light emitted from each light emitting element discussed in Japanese Patent Application Laid-Open No. 2009-179062, it is necessary to acquire an optimum correction amount for each light emitting element, resulting in complicated processing.